They should do petal, are they just single stemmed or bushy but with only foliage at the tips? Normal practice is to prune them back to around 4"- 6" when first planted if done in the autumn.
Blackstart

Petal
It sounds like you have bought hedging that has been grown as a 'standard'. I don't know if it will sprout from down the stem as you want but I would be inclined to plant and see. Keep the top growth trimmed when you trim the rest of the hedge and hope it fills out lower down.

Is there a reply please? Presumably I will not be pruning them according to Blackstart previous post?
My personal view is that they should be cut back to 4"-6" to encourage them to break and form bushy growth. However, I would normally plant them in the autumn so I am not sure how they will respond at this time of year. My gut instinct would be to prepare the ground well, plant them, prune them back and then make sure they do not suffer from lack of water. They should then put on new growth. Leaving them as they are risks having them growing as a single stem and not branching (apical dominance).
Blackstart

Thanks.The hedge plants were not grown or sold as standards. Buying the hedge plants at 4 foot high to extend and fill in gaps in my existing hedge was expensive and an awful shame to have to cut them right down. I might as well have bought small cheaper ones but different sizes with the existing would have looked unsightly. What shall I do please? petal

I presume you have planted them by now so I would leave them alone and cut them back early spring if required. Pity we cannot upload pictures as it would be very helpful. I wonder if you can PM me a photo?
Blackstart